Refrigerating apparatus



Jan. 2, 1945. J. L. GIBSON REFRIGERATiNG APPARATUS Filed Au 20, 1943 IN V EN TOR.

Patented Jan; 2, 1945 I UNITED STATES PATENT OFFlCE REFRIGERATING APPARATUS J Lowell Gibson, Dayton, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware compressor.

tional to the evaporator temperature or pres-- Application August 20. 1943, Serial No. 499,319

4 Claims. (Cl. 62-3) This invention relatesto refrigerating apparatus and more particularly to control means therefor.

In the past it has been necessary to build a motor-compressor unit with a sufflciently large motor and suitable controls so that it will operate at the highest suction pressure which may be reasonably expected to be encountered. The reason for this is the torque requirements of the motor increase with a rise in the suction pressure because more refrigerant is compressed per revolution. The suction pressure is normally the pressure on the low side or the evaporator of the refrigerating system which varies with the temperature of the evaporator.

. The highest suction pressure is normally encountered when the refrigerating system shuts down on a hot day until the evaporator temperature reaches room temperature and then the system is returned to operation. On such a day the evaporator temperature may be ashigh as 85 or 90 F. with a pressure of 93 to 100 lbs. per square inch. The suction pressure encountered in normal operation is much lower and is the greatest at the start of each running cycle of the This suction pressure is proporsure at the starting. cycle which may be 35 F. corresponding to an evaporator pressure of 33 lbs. If the motor-compressor unit is designed to operate at its maximum capacity and emciency, when the suction pressure is 93 to 100 lbs. per square inch, it will be only lightly loaded under normal operating conditions with a suction pressure of 33 lbs. or less. Inasmuch as the first cost of motor-compressor units is considerable and increases with an increase in size and capacity, this represents an investment, a great part of which is not used under ordinary conditions.

It is an object of my invention to provide a control means for amotor-compressor unit which will permit the unit to be designed to operate at its maximum capacity under normal operating conditions.

It is another object of my invention to provide a control ,means for a motor-compressor unit which will permit overloading of the unit as long as the motor temperature is below a maximum safe temperature limit.

It is another object of my invention .to provide a control which will permit loading up to the maximum safe temperature limit of the motor. 'According to my invention, these objects are attained by providing a suction line valve at the 55 suction entrance of the compressor which is controlled in accordance with the temperature of the compressor motor or the sealed motor-coinpres sor unit so that when the temperature of the motor or the unit approaches a-maxlmum safe temperature limit the suction line valve will throttle to reduce the suctionpressure or to prevent its rise.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred form of the present invention is clearly shown.

In the drawing:

Fig. 1 is a diagrammatic view of a refrigerating system including a thermostatic suction line control valve in section; and

Fig. 2 is a fragmentary view taken along the line 2 of Fig. 1.

Referring now to the drawing, there is shown in section a sealed motor-compressor unit 20 containing a rotary compressor 22 to which is directly connected the rotor 24 of an electric motor which has its stator 23 in heat exchange relationwith the metal casing 28 of the sealed unit taining a medium to be cooled. The liquid refrigerant in the evaporating means evaporates to cool the medium within the compressor 38 and the evaporated refrigerant is returned through the suction conduit 40 directly to the compressor in most refrigerating systems.

, .Where the condenser is air-cooled, the pressure in the condenser varies with the temperature of the air. If it is water-cooled, the con- .densing temperature will vary with the temperature of the water supplied. This variation does cause theload on a sealed unit to increase with the temperature rise'but this temperature variation and the change in load is quite small as compared to a change in temperature of the evaporator 38 and the change in load resulting therefrom. The reason for this is that under ordinary operating conditions the pressure and temperature of the evaporating means 36 is considerably below room temperature. This may be as low as F. corresponding to an evaporator pressure of about 9 lbs.-. If the system is shut down for a considerablelength of time the evaporator will rise substantially to room temperature which may be as high as 85 to 90 F. corresponding to an evaporator pressure of from 93 to 100 lbs. per square inch. If the evaporated refrigerant is allowed to flow directly from the evaporator into the compressor the compressor motor must be built large enough and powerful enough to operate with a suction pressure of 100 lbs. per square inch, whereas it may operate normally with a suction pressure of as low as 9 lbs. per square inch.

To build a motor-compressor unit for a certain refrigerating requirement at a suction pressure of 9 lbs. which must be designed to accommodate a. suction pressure of 100 lbs. under starting conditions, requires a very large and powerful motor to operate the compressor when the system is placed in operation after being idle for a suflicient length of time for the evaporator 36 to reach room temperature. On the other hand to obtain sufflcient capacity to perform the amount of refrigeration required under normal operating conditions of 9 lbs. suction pressure, requires a large compressor, because of the low density of the refrigerant drawn into the compressor. These factors therefore require a large compressor and a still larger motor which causes the cost of the motor-compressor unit to be very high in proportion to the amount of work normally done by the motor-compressor unit.

It is well-known that electric motors may be heavily overloaded when they are cool, but their load must be limited under normal operating conditions to prevent their temperature from becoming too high since the insulation of the windings is likely to be damaged if the temperature rises above certain maximum safe temperature. I propose to take advantage of this characteristic. When the refrigerating system is shut down for a considerable period of time the sealed motor-compressor unit will cool to room temperature. This will make it possible to heavily overload the motor upon starting but this heavy overload will rapidly heat the motor and theload must be rather quickly reduced as the temperature of the motor rises.

To allow the compressor motor and the sealed motor-compressor unit to operate upon the A greatest suction pressure and at the highest load without exceeding the maximum safe temperature limit, I provide a suction line throttling valve 42 having an inlet connection 44 to which the suction line 40 connects and an outlet connection 46 which connects to a second section 48 of the suction line extending to the inlet 50 of the compressor 22. This suction line valve 42 is controlled inaccordance with the temperatures of a thermostat bulb 52 which is fastened directly to the outer casing 28 of the sealed unit 20 directly adjacent the stator 26 of the compressor motor by a clamp 54. By placing .the thermostat bulb 52 in such position the heat from the motor can readily flow from the stator 26 through the metal wall of the casing 28 to the bulb 52.

When the compressor motor and the sealed unit become warm and approach the maximum safe temperature limit, the thermostat bulb will tend to close the valve 42 so as to gradually reducethe pressure in the section 48 of the suction line which feeds the .inlet 50 of the compressor 22. In this way. the suction pressure of the compressor will be reduced as the temperature of the compressor motor rises to prevent th motor temperature from exceeding a safe, limit. The valve preferably will be closed when the safe temperature limit is reached.

The thermostat bulb and the valve may be or a variety of forms andv systems of operation to perform this work. I have illustrated one form of construction which may be used. The main valve body 60 is provided with a stationary sleeve 62 which is held in place by a spider ring .64 and the bottom wall of the valve chamber 66. The spider rin 64 supports an adjustable spring retainer 68 for varying the tension upon a conical coil spring 10 bearing upon a plate 12 which serves both as a spring retainer for the spring Ill and as a bellows follower. for the bellows 84 which is located in the bellows chamber provided in the valve body 66 below the valve chamber 66. Connected to and movable with this plate I2 is a sleeve 14 which fits within the stationary sleeve 62. The sleeves 62 and 14 have register: ing slots 16 and 11 which register when the thermostat bulb 52 is substantially at normal room temperatures. When so registered the slots allow the evaporated refrigerant to enter the inlet M and to pass through the conical screen and through the slots i6 and H, the outlet connection 46 and the suction line section $8 to the compressor inlet 58 substantially without any throttling.

The interior of the bellows lid is connected by capillary tubing 82 to the thermostat bulb 52. The bellows 8d, the capillary tubing 82 and the thermostat bulb 52 preferably are filled with a hydraulic thermally expansible liquid. The amount of the charge of the hydraulic liquid as compared to the space provided will determine the temperature at which the valve begins to throttle the suction gas. The thermal coemcient of expansion of the liquid and the volume of the bulb 52 as compared to the bellows 84 will determine the temperature and rate at which the valve will close. The bellows 84 will expand with a rise in temperature of the sealed unit 20 and particularly the stator 26 of the electric motor which contains the insulated windings. The expansion of the bellows 84 will raise the plate 12 and the sleeve 14 so as to move the slots 11 in the sleeve 14 gradually out of registration with the slots 16 in the outer sleeve 62. This will gradually throttle the refrigerant flowing from the suction conduit 40 into the section 48 of the suction conduit 40 to gradually reduce the pressure in the section 48 to gradually reduce the suction pressure of the compressor 22 at the inlet 50 in accordance with the temperature of the stator .26 and the sealed unit 20. The temperature at which this takesplace should be varied in accordance with the heat resisting propertiesv of the electrical insulation used upon the windings.

When the system is idle, all parts will be substantially at room temperature and the suction line valve 42 will be fully open allowing the evaporated refrigerant in the evaporator to exert its full pressure at the inlet 50 of the compressor 22. The motor 26, being cool, will be able to accommodate a large overload upon starting and will be able to make it possible for the sealed unit to compress refrigerant rapidly. This will cause the stator 26 andthe sealed unit 2|] to rise rapidly in temperature. This rise in temperature will cause the heating of the thermostat bulb 52 and a rise in temperature of the f refrigerating thermostatic system to cause the valve 42 to gradually throttle the flow of refrigerant to the inlet 50 of the compressor 22. The relationship of the temperature of the stator 26 and the .sealed unit 20 to the opening of the valve 42 tem -may be provided with a suitable thermostatic switch to control the starting and stopping of the motor compressor unit in accordance with requirements. Also a current overload protector should be provided to protect the motor from overloads which may occur because of conditions other than high suction pressure. While I have shown my invention as applied to a refrigerating system having a sealed motor-compressor unit, it is also applicable to systems wherein the motor and compressor are in separate casings. 7

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form,it is to be understood that other forms might be adopted, as may come within the scope of theclaims which follow. v What is claimed is as follows:

1'. Refrigerating apparatus including a refrig erant circuit comprising condensing and evaporating means and a sealed motor-compressor unit for withdrawing evaporated refrigerant from the evaporating means and delivering compressed refrigerant to the condensing means, and a thermostatically controlled throttling valve a prede- 2. Refrigerating apparatus including a re- ,frigerant circuit comprising condensing and evaporating means and a sealed motor-compressor unit for withdrawing evaporated refrigerant from the evaporating means and delivering compressed refrigerant to the condensing means, and a thermostatically controlled throttling valve means located in said circuit and responsive to the temperature of said unit for gradually throttling in increasing amounts the vapor drawn from said evaporating means by said compressor as the temperature of said unit rises and approaches the assumed safe temperature limit.

3. Refrigerating apparatus including a refrigerant circuit comprising compressing, condensing and evaporating means, an electric motor for operating the compressing means, and a thermostatically controlled throttling valve means in said circuit between the evaporating and compressing means responsive to the tem-,

perature of said electric motor for throttling the ture.

4. Refrigerating apparatus including a refrigerant circuit comprising compressing, condensing and evaporatingmeans, an electric motor for operating the compressing, means, and a thermostatically controlled throttling valve means in said circuit between the evaporating and compressing means responsive to the temperature of said electric motor for gradually throttling in' increasing amounts the vapor drawn from said evaporating means by said com- .pressor as the temperature of said motor rises and approaches the assumed safe temperature limit.

' J LOWELL GIBSON. 

